This invention relates to gas ionization devices and, more particularly, to gas ionization devices having the capability of shifting or transferring data.
Gas ionization (plasma) charge transfer devices of the type described in U.S. Pat. No. 3,781,600, issued Dec. 25, 1973, to Coleman and Kessler have the advantage of wide flexibility of use. One method of fabricating such devices is explained in U.S. Pat. No. 3,810,686, issued May 14, 1974, to Coleman. Both patents are assigned to NCR Corporation, and are incorporated by reference. Such devices are operable as memory registers, as recirculating registers or as display devices, and either in a static or a dynamic mode. As described in the above Coleman and Kessler U.S. Pat. No. 3,781,600, a linear charge transfer channel can be operated in parallel with similar channels to form alphanumeric characters and can be expanded to increase the number of characters in a line without increasing the address electronic cost.
The plasma charge transfer device described in the Coleman and Kessler patent is shown in FIG. 1 in the form of a four-phase shift register 10. The shift register 10 comprises enclosure-forming plates 12--12 of any suitable dielectric material, such as clear glass, which define a channel 13 containing an ionizable gas such as neon and nitrogen. A plurality of transfer electrodes 14--14 (which may be transparent) are located on inner walls 16--16 of the plates opposite one another in parallel, but laterally offset relationship to subject the ionizable gas to an electric field when a suitable potential is applied across any two opposing electrodes.
Input electrode I and erase electrode E are located at opposite ends of the linear transfer electrode array. In the embodiment shown, all transfer electrodes 14--14, but not the input electrode I or the erase electrode E, are coated with a dielectric layer 18. The ionizable gas between any two adjacent opposing electrodes, including input electrode I and the nearest opposite transfer electrode, or the erase electrode E and the nearest opposite transfer electrode effectively forms a gas cell that is dischargeable when subject to a suitable potential.
Binary information is entered into the device 10 at the first cell, which is formed between the input electrode I and the nearest electrode 1. Whether the binary information entered at a particular clock time is a 1 or a 0 depends upon whether or not the voltage across the first cell exceeds the gas discharge or firing voltage, V.sub.f. The binary information is stepped along the device by the transfer electrodes 14--14 to a display position or to an output position at the opposite end of the device, then is shifted out of the device at the erase electrode E.
Operation of the device 10 is controlled by the pulsing and magnitude of the voltage, V.sub.i, applied to the input electrode, the voltage V.sub.s applied to the transfer electrodes, and the voltage V.sub.e applied to the erase electrode, and by the magnitude of the voltage V.sub.wc. V.sub.wc results from the charge Q.sub.wc deposited on the dielectric walls 19--19 by the firing or discharge of a cell. These voltages are chosen so that: EQU V.sub.i &gt;V.sub.f ( 1), EQU V.sub.s &lt;V.sub.f ( 2), EQU V.sub.i -V.sub.s &lt;V.sub.f ( 3), EQU V.sub.s +V.sub.wc &gt;V.sub.f ( 4).
As indicated by equations (1), (2) and (4), input voltage V.sub.i is greater than the discharge voltage V.sub.f, and sustaining voltage V.sub.s is less than V.sub.f and will not cause discharge unless combined with V.sub.wc. A combination of voltages, gas compositions, and gas pressures suitable for the operation of the shift register 10 is given here by way of example only. The voltages are V.sub.f .about.180 v, V.sub.i .about.200 v, and V.sub.s .about.160 v. A typical pulse width is 20 microsec. The ionizable gas is 100% Ne. The gas pressure is about 300 millimeters of mercury.
The device 10 is arranged to receive digital information every fourth clock time, at t=1, 5, 9, etc. The transfer electrodes 14--14 are connected as four sets--1, 2, 3, 4--each of which is normally maintained at V.sub.s, and is pulsed to 0 v. every fourth clock time. The electrode sets 1, 2, 3 and 4 are pulsed to 0 v. at t=1, 5, 9, etc.; t=2, 6, 10, etc.; t=3, 7, 11, etc.; t=4, 8, 12, etc.; respectively, and are maintained at V.sub.s at other times. Thus, if the input electrode I is pulsed to V.sub.i at any time other than t=1, 5, 9, etc., the voltage V.sub.s on electrode 1 opposes V.sub.i and equation (3) applies to preclude the first cell from discharging.
For convenience, each member of a group of four adjacent transfer electrodes 1, 2, 3, 4 is identified by a subscript which is the group number. The group numbers are arranged in ascending order from the input end to the erase end of the channel 16. The group nearest the input electrode is thus 1.sub.1, 2.sub.1, 3.sub.1, 4.sub.1,; the last group is 1.sub.n, 2.sub.n, 3.sub.n, 4.sub.n. See FIG. 1.
To enter a digital "1" into the device 10 at time t=1, 5, 9, etc., the input I is taken to V.sub.i so that, with the electrodes 1 at 0 v., equation (1) applies to the first cell I-1.sub.1, and discharge occurs there. If a digital "0" is to be input, the input electrode I is allowed to remain at 0 v. The digital "1" discharge applies positive charge of voltage V.sub.wc to the cell wall having the lower polarity. In this case, the lower polarity wall is associated with electrode 1.sub.1.
The wall charge shortly extinguishes the discharge. However, the timing of the 1234 sequence of transfer electrode pulsing is selected so that electrodes 2 are taken to 0 v. and electrodes 1 back to V.sub.s before the wall charge dissipates. Because of this 0 v. potential on electrode 2.sub.1 and the V.sub.s and V.sub.wc voltages on electrode 1.sub.1, equation (4) applies and the cell formed by the electrodes 1.sub.1 -2.sub.1 discharges. Discharge again leaves positive wall charge on the lower polarity wall, here the wall of electrode 2.sub.1. Again, the wall charge extinguishes the discharge and the associated voltage, V.sub.wc, is algebraically added to V.sub.s to discharge the next adjacent cell, which is formed by the electrodes 2.sub.1 -3.sub.1. This sequential transfer of discharge and wall charge continues as long as the sequential 1234 pulsing of the transfer electrodes prevails. Consequently, the information entered at the first cell can be transferred to a desired position within the channel or to the erase electrode E for destruction.
Note that the sequential pulsing of the transfer electrodes 14--14 occurs during the input of information as well as during transfer thereof. This permits previously entered information to be transferred serially along the device simultaneously with the entering of additional information which may occur once every four clock times of the transfer electrodes.
If it is desired to stop the shifting of information and to retain the information in place at any time, the sequence of transfer pulses is changed to what Coleman and Kessler refer to as the "hold" mode. One such sequence involves alternately pulsing two adjacent sets of the electrodes, such as sets 3 and 4, while the other two sets are maintained at a constant voltage.
A 14321234 hold sequence is taught in U.S. Pat. No. 4,051,409 issued Sept. 27, 1977 to D. G. Craycraft and assigned to NCR Corporation. The Craycraft hold sequence prevents charge build up on electrodes adjoining the display cells and thereby facilitates shifting charge information after the hold sequence without reloading.
After the load sequence, shifting is reinstated when desired by reverting to the 1234 sequence of transfer electrode pulsing.
Shifted information is erased as it reaches the erase electrode E by applying the voltage pulse sequence of the transfer electrodes 1 to the erase electrode. Upon discharge of the next to the last cell in the device (the cell formed by the electrodes 3.sub.n -4.sub.n adjacent the erase electrode E), positive wall charge is formed on the wall of the electrode 4.sub.n. Then, upon discharge of the last cell, 4.sub.n -E, the positive wall charge is transferred to the direct-coupled erase electrode and "extinguished" by the ground potential on the erase electrode.
The device 10 may be utilized either as a shift register memory or as a display device. The hold mode gives the device memory. When used as a shift register memory, the input pulse, resulting discharge, and associated wall charge (or their absence) represent a bit of binary information which is transferred along the device by the above-described charge transfer mechanism. As mentioned, the presence of the input pulse represents digital "1" and the absence of an input pulse represents digital "0" (or vice versa) as information is clocked into the register and transferred out. The information is transferred along the length of the device 10 until it is coupled to the output location where it can be read optically or electrically. For example, when a bit of information reaches the last cell position, the discharge there can be read optically by a conventional photodetector which produces an output signal that is read by any suitable device. Alternatively, the discharge can be read by direct electronic sensing of the charge transferred from the last electrode position to the erase electrode.
Because light is a by-product of the gas discharge, the device 10 can be used as a display in which the input pulse is transferred serially as described above. The absence of an input pulse forms an unlighted or blank cell or dot on the display, whereas an input pulse results in a lighted cell or dot. The displayed information can be loaded into the device and then held in place to provide a stationary display, or may be shifted continuously across the device. As mentioned previously, the single channel device 10 can be operated in parallel with similar devices so that the cells or dots form readable alphanumeric characters.
The plasma charge transfer device 10 of FIG. 1 is exemplary of the present state of the art in its use of three electrodes for input and keep-alive functions. The single input electrode I may be directly coupled to the ionizable gas (FIG. 1) or covered with dielectric 18 and thereby capacitively coupled to the gas (FIG. 2) in the same manner as the transfer electrodes 1, 2, 3 and 4. In this latter case, an input voltage of greater magnitude is likely required.
The pair of electrodes KA.sub.1 and KA.sub.2 shown in FIGS. 1 and 2 form a keep-alive cell. The keep-alive electrodes are capacitively coupled to the gas and connected to a source of alternating voltage of sufficient magnitude and frequency to repetitively discharge the gas within the keep-alive cell. This provides a sufficient supply of ionized particles to insure discharge of the cell formed by input electrode I and the first transfer electrode 1.sub.1 and thereby to insure the input of data into the shift register or display.
The above-described three-electrode keep alive-input arrangement is effective. There are disadvantages however. The three electrodes are somewhat cumbersome and require separate input and keep-alive circuitry. The life of the DC input electrodes can be shortened by sputtering effects. And, the large keep-alive electrodes necessitate weaving the input electrodes around them for external connection.